Photosensitive device



Oct. l2, 1937. E. DE W. wlLsoN 2,095,783

PHOTOSENSITIVE DEVICE Original Filed Dec. l, 1951 I n Mun/00:5. y

INVENTOR Earl D Wilson ATTORNEY l Patented Qct. 12, 1937 UNITED STATES PHOTOSENSITIVE DEVICE Earl De Witt Wilson, Wilkinsburg, Pa., assignor to Westinghouse -Electric & Manufacturing Company, a corporation of Pennsylvania Application December 1, 1931, Serial No. 578,399 Renewed March 17, 1937 Claims.

My invention relates to photo-sensitive devices and has particular relation to photo-sensitive devices of the dry photo-voltaic type.

Photo-voltaic cells constructed and operated according to the teachings of the prior art, of which I am aware, are of several types. One type of cell well known in the art comprises a copper disc having disposed thereon a layer of copperoxide transparent to ordinary light radiations. Contact is made with the copper oxide through a grid, preferably of spiral structure, that is rigidly clamped against the oxide surface.

In such a cell the photo-electric effect apparently takes place on the inner surface of the copper oxide, that is to say, at the interface between the pure copper surface and the oxide surface. The light is evidently transmitted through the copper oxide and its effect is evidenced by a flow of an electron current from the copper oxide to the copper or a flow of a conventional current from the copper to the copper oxide.

Another type of cell which is well known in the art comprises a solid plate of cuprous oxide which is produced by converting a copper metal plate completely to the oxide by suilicient baking. On one surface of this plate a translucent film of metal is disposed. Contact is made with the film of metal on one surface and with a conducting layer of material sprayed on the other surface of the copper oxide, and when the unit is subjected to the influence of illumination, an electron current flows from the copper oxide to the translucent film of metal.

In experimenting with these cells I have found that the current which ows in the last named cell between the copper oxide and the translucent film of metal is considerably greater than the current which ows in the first named type of cell between the copper oxide and the copper. On the other hand, I have found that the copper oxide disc which of necessity must receive rather careful treatment is an expensive'unit, and for this reason is not at all adaptable to the ordinary commercial uses to which the photo-voltaic cell is, at the present time applied. My experiments also have led me to the conclusion that, in general, the electron emission excited by light energy in the cells of the photo-voltaic type takes place by reason of some property of the copper oxide and the electrons are emitted by the copper oxide. The direction of emission and its magnitude are probably dependent on the surface in which the light impinges and is absorbed, on the 55 magnitude of the impinging illumination and on (Cl. 13B-89) the intimacy of the contact between the absorbing surface and its juxtaposed conductor.

It has been the practice in the art to designate the photo-electric effect which is attained when the current flows from the photo-sensitive material to its metallic backing as the "reverse effect and the effect which is attained when the electron current flows from the photo-sensitive material to the contacting film as the obverse" effect. Applying these designations to the conclusions of the discussions given hereinabove it appears that, in general, the obverse effect is considerably more marked than the reverse effect.

It is an object of my invention to provide an inexpensive photocell of the photo-voltaic type wherein the electron current Yshall ow away from the metal on which the photo-sensitive material is deposited.

Another object of my invention is to provide a photo-voltaic photo-sensitive element that shall be inexpensive to manufacture on large quantities of the type wherein the emission, arising by reason of impinging radiations, takes place from the surface of the photo-sensitive material facing the source of radiation.

Still another' object of my invention is to provide an inexpensive process for preparing a photo-voltaic cell of the type wherein the electron emission takes place from the surface of the ma.- terial facing the source of radiation that excites the emission.

A further object of my invention is to provide a simple and inexpensive process for preparing a photo-voltaic cell of the obverse type.

More concisely stated, it is an object of my invention to provide an inexpensive photo-voltaic cell that shall yield considerable power as compared with the cells of the prior art and that shall be so inexpensive to manufacture on a commercial scale as to be capable of general commercial applicability.

According to my invention I provide a cell comprising specifically, a copper plate having deposited thereon a layer of copper oxide. The copper copper-oxide plate is treated in a manner that shall be described hereinafter and after such treatment it is subjected to a discharge in an atmosphere of a highlyA raried argon. The discharge takes place preferably between a silver plate and an ordinary electrode and the silver plate is so disposed relative to the copper oxide surface of the copper copper-oxide plate that a film of silver is sputtered on the surface thereof. 'The plate, thus prepared, is provided with suitable elements for contacting the silver lm and the copper surface.

I have found that, when such a unit is connected through a suitable meter and is subjected to the inuence of light, an electron current ows from the copper oxide to the sputtered silver and is returned through the metal and through the copper to the copper oxide. 'I'he current is several times as large as the current of opposite polarity which iiows in the cells of the prior art in which the photo-electric effect apparently takes place at the interface of the copper and the copper oxide. On the other hand, the preparation of the unit requires very little in the way of skill in operation or elaborate treatment and is, consequently, considerably less expensive than the pure copper oxide unit provided in accordance with the teachings of the prior art.

The novel features that I consider characteristic of my invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and its method of operation, together with additional objects and advantages thereof, will best be understood from the following description of a specic embodiment when read in connection with the accompanying drawing, in which,

Figure 1 is a view partly in perspective and partly in section showing an embodiment of my invention.

Fig. 2 is a view 'partly in section and partly diagrammatic showing a complete cell constructed according to my invention and provided with the elements necessary for incorporating it in a closed working circuit.

Fig. 3 is a view in section showing a container wherein my cell is treated in the preparation thereof.

Fig. 4 is a graph showing a series of current illumination curves for a cell constructed in accordance with the teachings of my invention, and

Fig. 5 is a graph showing a voltage illumination curve for a cell constructed according to my invention.

The apparatus shown in Fig. 1 comprises a copper plate I having a layer of c'opper oxide 3 deposited thereon. In general, the copper copperoxide plate I may be produced simply by oxidizing one face of an ordinary copper plate. However, it may be of a structure similar to that utilized in ordinary rectifying apparatus and may be produced and treated by the same process as is utilized in the production and treatment of copper copper-oxide rectiiiers. As shall be seen hereinafter, it may be of advantage to destroy the rectifying property of the plate but this object can be accomplished after the plate is produced.

On the surface of the copper oxide a thin film 5 of sputtered metal, preferably silver, is deposited. The film 5 of metal is so thin as to be substantially transparent but for certain applications of my invention a translucent iilrn is suitable.

The layer 3 of copper oxide on the other hand, should preferably be so opaque as to prevent the transmission of light to the interface and thus to prevent the production of an electron current flowing in a direction opposite to the current for which the plate is particularly provided.

In Fig. 2 a photocell constructed according to the teachings of my invention is shown as connected in an electric circuit. 'I'he system shown in the view comprises a disc 1 of the type shown in Fig. 1 having an opening 9 therein. Electrical contact is made with the sputtered metallic lm 5 on the surface of the copper oxide layer 3 through a Washer II which is clamped to the sputtered film 5 by a bolt I3. The bolt I3 passes through the opening!! in the plate; and its lower threaded surface I5 is engaged by a nut I'I that in turn is so tightened as to engage the lower surface of an insulated washer I3. By the clamping action of the nut I'I and bolt I3 the insulated washer I9 is clamped against the copper surface of the photo-sensitive disc 'I while th metallic washer II is clamped against the conducting film 5 on the surface 3 of copper oxide.

A lead 2| is soldered to the lower surface of the copper element I of the disc I while a second lead 23 is firmly secured to 'the nut I1 that engages the bolt I3. When the device is utilized simply for the measurement of illumination the circuit through theelements of the disc may be completed through a suitable meter 25. The polarity of the electromotive force set up by the disc under the iniiuence of light is illustrated by the conventional symbols in Fig. 2.

According to my researches the photo-sensitive plate 'I may be best provided by suitably treating a. copper disc of which one surface has been oxidized. I have found that after the surface is oxidized the disc should be subjected to several mechanical impulses of considerable magnitude. This object can best be accomplished by depositing the plate on a table placing a wooden block on top of it and hammering the block substantially rwith an ordinary hammer.

While I am not certain as to the theoretical reasons for the improvement which is attained by hammering the plate my conjecture is that by such treatment the tendency of the plate to produce an electron current flowing from the copper oxide to the copper base is destroyed. It has been found that hammering destroys the rectifying property of a copper copper-oxide disc and according to present theories there is a definite relation between the photo-electric property of a copper copper-oxide disc and its rectifying property.

After having been subjected to the mechanical impulses the plate is alternately dipped into an acid bath and into iiowing water until the oxide acquires a glassy cherry red surface. The bath may be preferably concentrated nitric acid. After the plate assumes the proper appearance as described hereinabove, it is thoroughly rinsed and dried, care being taken at the same time, not to deposit any foreign material on its surfaces.

The sputtered iilmis deposited on the plate in a container 25 equipped with an outlet 26 whereby it may be exhausted. 'I'he copper copper-oxide plate is mounted on a stopper 21 provided with a ground surface to engage the ground internal boundary 29 of a conoidal shaped opening in the container 25.

The copper copper-oxide disc is rigidly secured to aheavy copper block 3| that is in turn fastened to a plurality of rods 33 welded in a stem 35 projecting from the stopper 21 for the container 25. In practice it is desirable that the edges of the disc shall not be sputtered and I have provided a suitable mask 31 that is mounted on the copper copper-oxide disc after the latter is secured to the copper block 3|. 'I'he block 3l is of such size that the copper copper-oxide disc is prevented from becoming hot when subjected to the influence of the sputtering apparatus.

A silver plate 39 is disposed parallel to the copper oxide surface 3 of the disc and at a short distance therefrom. A lead 4I suitably welded in the Walls of the container 25 is connected to the plate 39 and provides a suitable connection to a power supply source (not shown).

'I'he electrode cooperating with the silver plate 39 is preferably a collar 43 suitably mounted on a constricted portion 45 of the stopper 21 provided for the container 25. A lead 41 connected to the collar 43 and welded to the walls of the stopper 42`| provides for the connection of the power supply source to the collar.

In the practice of my invention the container 25 is completely exhausted and then lled with argon at a low pressure. My investigations have led me to the conclusion that for the most desirable results the container 25 must be first evacuated as completely as possible. The pressure of the argon should be from .4 to .5 millimeter of mercury. This pressure may be measured if desirable with an ordinary gage. However, I have found that for all practical purposes the pressure may be suitably estimated by noting the character of the discharge through the gas.

After the container has been completely exhausted and suitably lled with the rarified argon the collar 43 is then connected to the positive terminal of or approximately 750 volt power source while the silver plate 39 is connected to the negative terminal thereof. A discharge is thus produced in the container and is continued for fteen seconds after which it is found when the disc is removed from the block 9|, that a thin layer 5 of silver has become sputtered on the surface 3 of the copper oxide.

In Figs. 4 and 5 graphs are shown giving the general characteristics of a photocell constructed according to my invention. In Fig. 4 the current transmitted by a cell in nulli-amperes `is plotted as ordinate while the light ux impinging on the cell in foot candles is plotted as abscissa.

As will be noted in Fig. 4 a family of curves 49, 5I, 53 and 55 is plotted. The parameter for the curves is the resistance connected in the circuit with the cell 1. The four resistances utilized in taking the curves 49, 5|, 53 and 55 shown in the view were respectively 1 ohm, 11 ohms, 100 ohms and 1000 ohms.

In Fig. 5 the voltage output of a cell constructed according to my invention in milli-volts is plotted as ordinate and the light flux impinging on the cell in foot candles is plotted as abscissa. The `curve 51 shows the characteristic of an average cell.

Indiscussing the features of my invention I have referred hereinabove, in general, to a photocell of the copper copper-oxide type. While my invention is specifically applicable to a cell of this type a number of the features discussed herein are equally as well applicable to photovoltaic cells of other types, such, for example, as the cell made up of an iron plate, a selenide deposited on the plate and a. silver deposit on the selenide layer. To the extent to which my invention applies to cells of other types it is understood that the applications of my invention to such cells are equivalents which lie within the scope thereof.

Again while discussing the elements of my invention I have referred, in general to silver as the preferable contacting material to be utilized with the copper copper-oxide disc. While I have found that silver yields highly satisfactory results, it is possible, that other metals may exist which would yield as satisfactory results or which would be applicable for cells utilized for a particular purpose. My invention is, therefore, not to be restricted to a cell incorporating only a silver contacting surface.

Although I have shown and described certain specific embodiments of my invention, I am fully aware that many modifications thereof are possible. My invention therefore is not to be restricted except insofar as is necessitated by the prior art and by the spirit of the appended claims.

I claim as my invention:

1. The process of preparing a photo-sensitive device of the copper copper oxide type which comprises the steps of preparing a copper plate to have a layer of copper oxide on at least one surface thereof, subjecting said plate to at least one mechanical impact and sputtering a layer photo-active therewith on the copper oxide surface.

2. The process of preparing a photo-sensitive device which comprises forming a copper-oxide layer oncopper, applying energyx to said copper and copper-oxide tending to destroy any rectifying action between said copper and said copper oxideand sputtering a layer of metal photo-active therewith on the copper-oxide surface.

3. The process of preparing a photo-sensitive device which comprises forming an opaque c'opper-oxide layer on copper and sputtering a layer of metal photo-active therewith on the copperi 

